Non-aqueous freestanding ion conductive gel for electrolyte of lithium secondary battery and preparation method thereof

Abstract

Proposed are a non-aqueous freestanding ion conductive gel for application to an electrolyte of a lithium secondary battery and a preparation method thereof. The non-aqueous freestanding ion conductive gel including: a matrix including a hydrophobic polymer famed through polymerization of monomers having an unsaturated double-bond; a domain dispersed in the matrix and including a hydrophilic ionic liquid; and a surface active layer including an ionic liquid having surface activity, in which a portion of a hydrophobic segment in a chain of the ionic liquid having surface activity is positioned in the matrix, and a portion of a hydrophilic segment in the chain is positioned in the domain. The gel has high ionic conductivity, high lithium ion transference number, and excellent mechanical strength. The gel can be used as an electrolyte of a lithium

What is claimed is: 
     
         1 . A non-aqueous freestanding ion conductive gel comprising:
 a matrix comprising a hydrophobic polymer formed through polymerization of a monomer having an unsaturated double bond;   a domain dispersed in the matrix and comprising a hydrophilic ionic liquid; and   a surface active layer comprising an ionic liquid having surface activity, wherein a portion of a hydrophobic segment in a chain of the ionic liquid having surface activity is positioned in the matrix, and a portion of a hydrophilic segment in the chain is positioned in the domain.   
     
     
         2 . The non-aqueous freestanding ion conductive gel of  claim 1 , wherein the non-aqueous freestanding ion conductive gel is a bi-continuous structure in which the matrix is a continuous phase and the domain is a continuous phase. 
     
     
         3 . The non-aqueous freestanding ion conductive gel of  claim 2 , wherein the domain forms its an ion channel. 
     
     
         4 . The non-aqueous freestanding ion conductive gel of  claim 3 , wherein the thickness of the ion channel varies depending on the content of the ionic liquid having surface activity. 
     
     
         5 . The non-aqueous freestanding ion conductive gel of  claim 1 , wherein the domain further comprises a lithium salt. 
     
     
         6 . The non-aqueous freestanding ion conductive gel of  claim 5 , wherein the lithium salt comprises at least one selected from the group consisting of lithium bistrifluoromethanesulfonylimide (LiN(CF 3 SO 2 ) 2 , LiTFSI), lithium perchlorate (LiClO 4 ), lithium hexafluorophosphate (LiPF 6 ), lithium tetrafluoroborate (LiBF 4 ), lithium bisfluorosulfonylimide (Li(FSO 2 ) 2 N), LiFSI), lithium triflate (LiCF 3 SO 3 ) lithium difluoro(bis(oxalato))phosphate (LiPF 2  (C 2 O 4 ) 2 ), lithium tetrafluoro(oxalato)phosphate (LiPF 4  (C 2 O 4 )), lithium di fluoro (oxalato) borate (LiBF 2  (C 2 O 4 )), and lithium bis(oxalato)borate (LiB(C 2 O 4 ) 2 ). 
     
     
         7 . The non-aqueous freestanding ion conductive gel of  claim 1 , wherein the monomer having an unsaturated double bond is represented by Structural Formula 1 below: 
       
         
           
           
               
               
           
         
         In Structural Formula 1, 
         R 1  is a C3-C20 linear or branched alkylene group or a C6-C30 arylene group, and 
         R 2  is each independently a hydrogen atom or a C1-C3 linear or branched alkyl group. 
       
     
     
         8 . The non-aqueous freestanding ion conductive gel of  claim 1 , wherein the ionic liquid having surface activity comprises an alkyl group having 8 or more carbon atoms. 
     
     
         9 . The non-aqueous freestanding ion conductive gel of  claim 8 , wherein the ionic liquid having surface activity comprises at least one selected from the group consisting of imidazolium-based ionic liquid, pyridinium-based ionic liquid, piperidinium-based ionic liquid, pyrrolidinium-based ionic liquid, ammonium-based ionic liquid, phosphonium-based ionic liquid, and sulfonium-based ionic liquid. 
     
     
         10 . The non-aqueous freestanding ion conductive gel of  claim 1 , wherein the hydrophilic ionic liquid comprises an alkyl group having 5 or less carbon atoms. 
     
     
         11 . The non-aqueous freestanding ion conductive gel of  claim 10 , wherein the hydrophilic ionic liquid comprises at least one selected from the group consisting of imidazolium-based ionic liquid, pyridinium-based ionic liquid, piperidinium-based ionic liquid, pyrrolidinium-based ionic liquid, ammonium-based ionic liquid, phosphonium-based ionic liquid, and sulfonium-based ionic liquid. 
     
     
         12 . The non-aqueous freestanding ion conductive gel of  claim 1 , having a thickness of 20 to 200 μm. 
     
     
         13 . An energy storage device comprising the non-aqueous freestanding ion conductive gel of  claim 1 . 
     
     
         14 . The energy storage device of  claim 13 , wherein the energy storage device is any one selected from the group consisting of a transistor, a super capacitor, and a lithium secondary battery. 
     
     
         15 . A method of preparing a non-aqueous freestanding ion conductive gel, the method comprising:
 (a) preparing a microemulsion comprising a hydrophilic ionic liquid, a monomer having an unsaturated double bond, an ionic liquid having surface activity, and a photoinitiator; and   (b) preparing a non-aqueous free-standing ion conductive gel by photopolymerizing the microemulsion.   
     
     
         16 . The method of  claim 15 , wherein the microemulsion comprises: 100 parts by weight of the hydrophilic ionic liquid; 10 to 80 parts by weight of the monomer having an unsaturated double bond; and 10 to 50 parts by weight of the ionic liquid having surface activity. 
     
     
         17 . The method of  claim 15 , wherein the microemulsion comprises 0.1 to 1 parts by weight of the photoinitiator per 100 parts by weight of the monomer having an unsaturated double bond. 
     
     
         18 . The method of  claim 15 , further comprising, (a′) preparing a mixture by mixing the hydrophilic ionic liquid with a lithium salt, (a′) being performed before (a), wherein (a) is a step of preparing the microemulsion containing the mixture, the monomer having an unsaturated double bond, the ionic liquid having surface activity, and the photoinitiator. 
     
     
         19 . The method of  claim 18 , wherein the lithium salt has a molar concentration of 0.1 to 10 M with respect to the sum of the hydrophilic ionic liquid and the lithium salt. 
     
     
         20 . The method of  claim 15 , further comprising (b′) injecting the microemulsion into a glass mold, (b′) being performed before (b).